JPS59124404A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve the durability of steel cord by specifying the dropping-in amount of an outside filament into an inside-layer circumscribed circle for each number of twist and specifying the shaping-rate for an outside-layer filament, in a tire reinforced by two-layer twist or three-layer twist steel cord. CONSTITUTION:In a steel cord constituted of 3 filamens in an l-layer inside and 9 filaments in an m-layer outside, the average value X, for the filaments 3 in the m-layer, of the max. value of the amount X of dropping-in in the direction of center over the circumscribed circle 4 of the inside layer l is set so that a prescribed equation is satisfied in accordance with the number of pieces in the l-layer, in the part where the filament 3 in the m-layer does not contact with the filament 2 in the l-layer, and a steel cord is constituted so that the shaping rate represented by the ratio between the diameter Dw of twist of the filament in the m-layer and the diameter Dr of steel cord becomes 90-110%. With such constitution, the durability of steel cord can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention improves the durability of steel cords in pneumatic radial tires, particularly by improving the arrangement of filaments in the two inner layers of steel cords having a two-layer or three-layer twist structure. This invention relates to a pneumatic radial tire that has been improved and has extended tire life.

In recent years, steel cords for tires have a twisted structure of p
xq (where p and q are expressed as integers of 2 or more) The so-called layered structure has changed to the layered structure, but the reason for this is that the latter is more complex than the former due to (1) mutual contact between filaments. The following advantages are mentioned: less fretting and less decrease in strength (2) high productivity per unit time.

Even in the case of a layer-twisted structure, a reverse-twisted (sz or zs) structure in which the inner and outer layers have different twist directions exhibits the same fretting condition as a layer-twisted structure, and no improvement effect is observed, or even if improvements are made. Preliminary breakage of specific filaments in specific layers was still observed, and the improvement effect was not sufficient.

Therefore, attempts have been made to apply steel cords with a layered structure in which the inner and outer layers are twisted in the same direction to pneumatic radial tires.
It is described in Publication No. 104.

However, in this case as well, conventional methods aimed at an ideal helical state, but did not take into account the effect of the outer layer filament falling into the inner layer space, as will be described later.Therefore, there was no fall, or even if there was, there was only a small fall. The problem was that the balance between the tension of the inner and outer layers during tensile deformation was poor, and stress concentration on the inner layer was unavoidable.

The invention of this application alleviates the concentration of stress on the inner layer during tensile deformation by dropping the filaments of the outer layer by a certain amount or more into the inner layer space in a steel cord with a layered structure, and also reduces the interaction of the filaments between the layers. The purpose is to suppress filament breakage and improve durability, prevent cord breakage in the tire belt layer and carcass ply layer, and extend the life of pneumatic radial tires. be.

That is, in the invention of this application, l and m are integers, l is 2 to 5, and under the range J<m<n, 1+m or ul
The two layers on the center side of the cross section of a steel cord with a two-layer twist or eight-layer twist structure, each expressed with the expression 10m+H, are the same as -
In a pneumatic shirashial tire reinforced with steel cords that have different twisting directions but different twisting degrees, the filament that makes up the outer m layer of the above two layers makes up the inner one layer. In the part that does not contact the filament group, m layers of filaments are arranged so that they fall inside the circumscribed circle surrounding one layer of filament group, and the maximum value of the amount of fall inward from the circumscribed circle for m filaments is calculated. When the average value in the tire product is 1 = 2 (-0,24k" + 0.46k)
d (round (-0,78k2+ 1.87k),
cl...(1) When 1=3 (-0,10
k2+ 0.24 k) (1<bill<(-0,31k2
+0.78k)d...(2) When 1=4 (-0.05k2+0.16k) d<father.

(-0,15k"+ 0..49k) d
...(8)! =5 (-0,02k"+0.
12 k) ti (round (, -0,06 to 2+0.8
5k) d...(4) Here: Ratio of twist pitch P of 1 layer to twist pitch P of m layer P□/P.

d: The filament diameter (am) is within the range of 90 to 110 m-layer filaments.
% range shaping is a pneumatic 9 radial tire reinforced with steel cord shaped in %.

In this case, y flow! is 2 and fC is 3, which is preferable because it has a high fall effect.

The invention of this application will be explained below with reference to the drawings.

FIG. 1 shows a cross-sectional view of a conventional two-layer twisted steel cord 1. In the figure, the number of filaments 2 in one layer inside is 3.
, and the number of filaments 8 in the outer m layer is nine. Although the two layers are shown with diagonal lines in different directions to distinguish them, they all have the same twisting direction, and the circumscribed circle that surrounds the group of filaments 2 in one layer on the inside is the same as the m layer on the outside. This is the case when the filament is not depressed. Second
The figure shows the locus of one filament of m layers in the steel cord shown in the figure.The part surrounded by two concentric circles 5 and 6 shows the locus, and is surrounded by dotted lines and solid lines. The small circles are the ends of the same filament's one-turn trajectory.

FIG. 8 is a sectional view showing an embodiment of the invention of this application.
Similar to the conventional example shown in Fig. 1, the number of filaments in one layer on the inside is 3, and the number of layer m on the outside is 9, but the portion where the filaments of the m layer do not come into contact with the filament group that makes up the entire layer. , a circumcircle 4 enclosing one layer of filaments
It is arranged so as to fall inward, that is, toward the center of the circumscribed circle beyond the circumference of the circumscribed circle. The fall t of the m-layer filament is the distance between the two tangents of the two circles at the two intersections C, C8, where the straight line g connecting the center of the filament's cross-sectional circle and the center of the circumscribed circle forms with the two circles. X
The maximum value of this X value is expressed as the average value ix for m filaments.

However, there is a limit to the amount of fall (X, therefore, the average value) of such an m-layer filament, and that limit value is determined by the stone cord structure, filament wire diameter, and twisting pattern, and this limit value is determined by the amount of drop X, which applies a large tensile force to the filament. This can be determined experimentally by twisting the cord while observing the cross section of the cord. The result is something like Figure 8! Two layers of twist expressed in ten meters or one more layer n
Add a layer fcj! In the three-layer twist represented by 10'm+n, the limit amount of the average value D of the above-mentioned fallen child, that is, the limit amount of fall, or L (home) is calculated by the following 4 formulas % formula % (5) (6) (7) (8 ) Here, it was found that k and d are shown as being the same as in formulas (1) to (4).

By the way, in conventional steel cords, there was no drop as shown in Figure 1, or the drop weight was an average value or a small value as shown by X in Figure 3, but the inventors have investigated the durability of the steel cord. Various research about? Over time, the average value of the drop in the steel cord of the tire product. (hereinafter simply referred to as product failure) exceeds the conventional value and exceeds a certain value, a significant improvement occurs in the durability of the steel cord from that stage, and related to this, the shape of the m-layer filament in the wire preform I also learned that the rate has a big impact on the durability of the above cord.

Here is a steel cord product that was taken out of a tire. This was determined by microscopic observation of the cross section of the cord, but in order to prevent filament movement during cross-section polishing, the coating rubber was peeled off from the outer surface of the cord and then embedded in a naturally hardening resin. The above observations were made after the specimen was fixed.

The shaping rate of the fcm layer filament is a numerical value expressed by the following equation using the measured values of the 9-9 diameter Dw of the m-layer filament obtained by loosening the steel cord and the steel cord diameter Dr.

The amount of product decline, including conventional steel cords, is at an all-time high. The durability of the steel cords was investigated based on the filament breakage rate after 200,000 hours of actual running on tires using steel cords with various values for the limit drop XL and the shaping rate. As a result, product decline:! Cross. and Rumi with a limit of 1 bill. / Compared to steel cords with XL of 14 or less, this is a bigger heaven. It was found that those having a ZXL ratio had a remarkable decrease in the breakage rate to 91% or less, and that filament shapes with a ratio in the range of 90 to 110% had a small breakage rate. father. /
When XL was 1/8 or less and the shaping rate was outside the range of 90 to 110%, breakage of the single-layer filament occurred first. In addition, in the conventional steel cord, X()/X was in the range of 0 to 1/4, and the filament breakage rate was about 8 layers.

Therefore, in order to improve the durability of the steel cord filament, the amount of drop in the product of TTL and M layer filament should be adjusted.
It is necessary to make b larger than the critical drop and smaller than the critical drop, and as this critical drop il XL changes with the number of l, the formula can be expressed as follows: This means that it is necessary to keep it within the range of (1) to (4).

Shading can improve the filament breakage rate by setting the rate in the range of 90 to 110%;
If the ratio is less than 0%, the M layer will tighten the 1st layer, increasing the interlayer contact pressure of the filaments of both sides and increasing the p-fretting.
Even if it is possible to reduce the thickness of the layer, it is quite difficult and the distortion becomes large, making it difficult to control the quality.

M-layer filament as above! The effect of causing the layer to fall within the circumscribed circle can be thought of as follows.

When there is a reverse twist relationship of S/z or Z/S, a specific helical filament in the outer layer contacts a group of inner layer filaments 2
Since the distance between the points is short, the part of the filament between the two points of contact forms an arc, but during tensile deformation, the arc is unlikely to extend into a chord, and tension will not concentrate in the inner layer. Although it is hard to 9, it does not prevent durability from decreasing due to fretting.

On the other hand, fretting is improved when S/S fc has a Z/Z same direction twist9 relationship, but if the spacing between the two contacts in contact with the inner layer of the m-layer filament, that is, the 1-layer filament group, is reversed. 9. Since the length is considerably longer than in the case of a twisted relationship, when the steel cord is tensilely deformed, the m-layer filament is deformed so that the arc between the two contact points becomes a chord instead of deformation in which the filament itself stretches.9. M layers of filaments fall into the twisting space of 1 layer. If such deformation becomes significant, the filament of the 91st layer will share more of the tension than the filament of the m layer, and t) the IN filament will break first. Therefore, it is understood that such an imbalance in tension sharing can be prevented by lowering the m layer to a certain extent from the beginning.

Also, in terms of shading, if the shading is insufficient or excessive, the elastic deformation of the cord will be alleviated and the cord will move, which will exert a force on its inner and outer layers. In that case, the shading becomes so large that the ratio deviates from 100%, so from this point of view as well, it is necessary to keep the shading close to 100%. Note that this force (initial contact force) exerted on the inner and outer layers is added to the tensile contact force that often occurs when each layer tightens when the cord is pulled, and acts as a friction force when the filaments mutually frett, so it should be as small as possible. preferable.

In addition, as a method for making the m-layer filament fall inside the circumscribed circle of the 1-layer filament group to within the range 0 of the invention of this application, for example, the tension of the m-layer filament during cord twisting may be increased (conventionally). At this time, care should be taken to ensure that the tension of each filament in the m layers does not become uneven.

4 and 6 show the trajectory of the m-layer filaments in the steel cord shown in FIG. It has a crushed shape rather than an annular shape.

The invention of this application will be explained in more detail with reference to Examples below.

Tires using various steel cords for the carcass, with different product drop amounts and 0 and shading, were prototyped, and the durability of the cords was evaluated through field running tests.

Is the tire size 1000R2014PR? , after putting it into a user who mainly drives on high-speed general roads and running it for 20,000 hours,
We took out the cord from the tire and examined the filament breakage rate. Forty cords were examined, and the filament breakage rate was calculated as number of broken filaments/total number of filaments x 100i.

The results are shown in Table 1. Among the comparative examples, Comparative Example 1 in particular is an example using a conventional steel cord. −X() /
, Compared to this, the filament breakage rate is clearly improved.

・Examples 7-8 Comparative Examples 11-18 Here, an example of application to a belt is shown.

When the tread encounters a penetration part while driving on a rough road, moisture enters through the penetration part, causing corrosion fatigue rupture of the outermost belt and the belt cord below it, which may lead to a burst. Therefore, the belt cord is also required to have high corrosion resistance or fatigue resistance. In order to fully confirm the effects of the invention of this application on belts, various product drop amounts and
All tires with a 3- and 5-belt structure in which a steel cord with a certain shape was applied to the 8th belt were manufactured as prototypes, and the belt cord breakability was evaluated after driving on rough roads. In the evaluation, the car was rehabilitated after driving on rough roads for 30,000 days, and after driving for another 30,000 hours (
Total mileage was 60,000.

Tire size: 1000R20 Belt structure 2 8.5 belt prototype Cord applicable belt layer: 8th belt Belt treat driving: 18.6 pieces 15 cr IL Belt angle: Left 72° Steel cord structure: 8+9+15X0.23+1 Twisting pitch: 6/] 2 /1 s/a, 5=”x/P
2: 0-5 However, the drop is in the 8-layer void of the 9-layer filament.

The cord breakability was evaluated by arbitrarily dividing the tire into six equal parts after running, and counting the number of broken third belt cords that were included in the divided parts. The smaller the index, the better the cord breakage 4 & crab.

The results are shown in Table 2. Comparative Example ] is an example using a conventional steel cord. Examples 7 and 8 clearly have improved breakability compared to the comparative example.

The invention of this application is a steel cord having a two-layer twisted or three-layer twisted structure, in which two layers on the center side of the cross section have the same twisting direction but different twisting pitches. In a reinforced pneumatic radial tire, the filaments of the outer layer of the above two layers are dropped by a predetermined amount inside the circumscribed circle surrounding the group of filaments of the inner layer, and the filaments of the outer layer By setting the shaping ratio within the range of 90 to 110%, the unbalance of tension in the same twist and direction can be improved without impairing the fretting improvement effect due to the same twist direction, resulting in a remarkable improvement in durability. As a result, the life of pneumatic radial tires using this steel cord for the carcass or belt can be significantly improved.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional two-layer twisted steel cord with the same twisting direction. Figure 2 is a cross-sectional view showing the trajectory of m-layer filaments of the cord in Figure 1. Figure 8 is a cross-sectional view of this steel cord. FIG. 4 is a cross-sectional view of a two-layer twisted steel cord in the same twisting direction of the invention of the application; FIG. 4 is a cross-sectional view showing the locus of m-layer filaments of the cord of FIG. 3; ]...Steel cord 2...1 layer of filament 3...m layer of filament 4...circumscribed circle surrounding 1 layer of filament group 5...m
The inner line of the filament locus of the layer 6...the outer line of the filament locus of the m layer. Patent applicant Brideston Tire Co., Ltd. Figure 1 Figure 2 Figure 8 Figure 4

Claims (1)

[Claims] LA and m are integers, l is 2 to 5, and 1 < m
In the range of <'n, two layers on the center side of the cross section of a steel cord with a two-layer twist or eight-layer twist structure, respectively expressed as l+m or l+m+n, are expressed as l0m. In a pneumatic radial tire reinforced with steel cords in which the layers are of the same twist direction but different in twist direction, the filament constituting the outer m layer of the two layers is on the inner side. In the part that does not contact the filament group constituting one layer, the m filaments are arranged so as to fall inward from the circumscribed circle surrounding the filament group of one layer, and the m filaments have the maximum amount of fall inward from the circumscribed circle. When the average value or the value of the tire product X□ is 1=2 (-0,24k8+0.46k)
(1<to〈(-0,78k”+1.87k) d
...(1) When 1=8 C-0,1Ok2+ 0
・g4k) d (tag (-0,81k"+0.78k) d
・(2) 4=4 @ (-o, osk”+o
, lt) d (round (-0,15 to 2+ 0.49°k
)d...(8) When J=5 (-0,02 to 2+'0.12k) d(x, ((-0,06k"+0
．． 85 k) a ... (4) Here: Ratio of twisting pitch P of one layer to twisting pitch P2 of m layer P., /P. d: 1) in the range of filament wire diameter (Ill, ),
A pneumatic radial tire characterized in that the m-layer filaments are reinforced by steel cords having a shaping ratio of 90 to 110%. λ! 2 or 8, the low pneumatic radial tire according to claim 1.